1. Field of the Invention
The present invention relates to the field of flying electric generators (FEG) and more particularly to a new configuration of auto-gyro rotor flying electric generators featuring wing lift augmentation.
2. Brief Description of the Related Art
The idea of flying electric generators is not new, and several methods of extracting energy from the high altitude winds have been proposed and are now in development. It is well known that the energy content in wind increases with distance from the ground (altitude). Current wind turbine technologies attempt to take advantage of this fact by reaching ever higher, but their cantilever design limits their maximum height, as large and costly steel and concrete bases are required to react against the bending forces introduced by their necessary structural geometry. Flying electric generators or FEGs in contrast require only a thin, light tether attached to a small ground anchor point to react against the force of the wind, and they can climb high above the ground and into the most concentrated and abundant natural energy source of the high altitude winds.
Currently, auto-gyro rotor based FEGs in development have at least four rotors, each having two or more rotor blades, with two rotors rotating in one direction, and two diagonally spaced rotors rotating in an opposite direction. The most commonly seen configuration is four rotors in a symmetric square pattern, with an X-shaped pattern similar to what is shown in FIG. 14. Alternatively, the rotors may be arranged so that the forward or upwind rotors do not interfere with the air flow to the aft or downwind rotors.
The auto-gyro rotor FEG flies up from the ground and hovers as a multi-rotor helicopter. For takeoff and hovering the FEG consumes electric power which is provided from a power grid or a generator on the ground, not shown, depending on the application. Electric power from the ground is transmitted through conductors in a tether and is used to create torque in drive motors for the rotors. These drive motors and their controllers are designed to convert electric power coming up the tether from the ground into torque to turn the rotors and also to convert excess torque available at the rotors into electrical energy to send down the same conductors in the tether for use on the ground. The rotors generate thrust by moving air downward, through the rotor disk. The amount of thrust is controlled either by rotational speed of the rotors, using a fixed pitch blade, or by varying the pitch of the blades while they are rotating at a constant rotational speed, or by a combination of the two techniques. As the rotors create thrust, they require torque input to rotate. The amount of torque required times the rotational rate of the rotor is the power required to maintain that level of thrust. The torque input to keep the rotor turning and create thrust also results in a reaction torque from the air against the rotor. This torque is proportional to the thrust, and because there are pairs of rotors rotating in opposite directions, this torque is normally balanced if each rotor is producing the same thrust.
It is possible to control an FEG rotation about a vertical axis, or yaw, by reducing the thrust of one pair of rotors rotating in one direction while increasing the thrust of another pair of rotors rotating in the opposite direction. If this is done to maintain the total thrust level constant, the FEG will only rotate in yaw, and maintain orientation about the pitch and roll axes, and its position. For the FEG to change orientation about the roll (longitudinal) axis or pitch (transverse) axis, the thrust is increased on the side of the FEG desired to rise, and decreased on the side desired to lower. Maneuvers can be combined as required, with roll, pitch and yaw rotations done simultaneously.
For an FEG to climb, overall thrust is increased and the FEG accelerates upward, descending is the opposite. For the FEG to move laterally, it is rolled or pitched so that a portion of the overall thrust vector is inclined in the direction desired, this component of thrust will accelerate the FEG in that direction. Once the FEG has accelerated to the desired travel speed in a direction, it is leveled out to maintain that speed. The FEG is stopped by rolling and or pitching in the opposite direction to the velocity until the FEG has decelerated to zero speed.
Once the FEG climbs to the generation altitude, where the wind speed is adequate to allow power generation, it flies downwind to a position where an angle of the tether with the ground is acceptable for the wind conditions and space available. The horizontal component of the tension in the tether now reacts against the force of the wind on the FEG, and this force will cause the FEG to naturally rotate in yaw like a weather vane to face into the wind. This is caused by an unbalance in drag from the unequally spaced rotors on each side of the tether, or a by vertical stabilizer placed aft of the tether attach point, or both. As the vehicle yaws to face the wind, the drag on each side balances and the vehicle will maintain a heading. Next, the FEG is commanded to gradually pitch up to a large angle of attack. The positive pitch angle of attack exposes the underside of the rotors to the wind. The thrust of the rotors now has a down-wind component, plus a vertical component.
The vertical component of thrust, plus the lift from the wings in the present invention, must remain equal to the FEG weight plus the vertical component of tether tension where it attaches to the FEG or the FEG will climb or descend. Because the rotor area now exposed to the wind has increased, the thrust also increases. The larger the pitch angle, the larger the exposed area and the larger the thrust. As the FEG angle of attack is increasing, the blade pitch of the rotors must be decreased to limit thrust increase, so that the vertical component of thrust does not increase. Increase in the vertical component of thrust is reduced by the increasing pitch angle, however, a practical maximum for the previous auto-gyro rotor FEG angle of attack was 45 degrees, the addition of wings to and FEG will allow a higher angle of attack, up to about 70 degrees. The inflow of the wind under the rotors applies a torque to the rotors, which drives them to a faster rotational rate, and this accelerating torque increases with reduced rotor blade pitch. To prevent the rotors from accelerating to a faster rotational rate, the electric motors apply torque in the direction against this acceleration, which creates electric power that is sent down the conductors in the tether for use on the ground. When the pitch maneuver is complete, the FEG is flying like a kite, with a large pitch angle of attack, and the tension on the tether tension and weight of the FEG will balance the force of the wind on the FEG.